Thanks everyone.
How? Stripped of all the fluff, it was deep resolve: Every single day, I decided not to drink alcohol.
My second brother's demise was still in the making, so I could see where this road went - and it was very, very dark. Cirrhosis, bleeds, yellowing, bloating, wasting, ambulances, ICU, induced comas, pain, misery, chaos, broken relationships, loss of everything.... By then it was clear that I'd be the last sibling standing and I decided in my cells that I did not to follow either of my brothers' paths. I took charge, and never touched it again.
Knowledge is power, I suppose.